The logic as explained to me is that the curved nature of 30+ round magazines sometimes causes the bullets to catch because of the "bullet tilt" and most mags ( including tapco mags) outside of PMAGs are more prone to this. I'm guessing this is why you see a lot of other brands tout that they have magpul followers in an effort to prevent this. I've never experienced this but just passing on what I was told.

This is why 20 "Thermelts" are generally good magazines. They are straight feed.